This invention relates to a method and composition for inhibition of corrosion of carbon steel storage and mixing tanks containing aqueous solutions of ammonium sulfate by addition thereto of small amounts of ammonium polyphosphate, sodium nitrite, potassium nitrite, ammonium thiosulfate, sodium thiosulfate or potassium thiosulfate. Ammonium sulfate, in the form of aqueous solution is useful as a fertilizer. The equipment employed in mixing and storing these aqueous fertilizer solutions is commonly constructed of carbon steel. However, aqueous ammonium sulfate solutions are acidic and as such, corrosive to equipment made of carbon steel. If such corrosion proceeds unchecked, damage to equipment, contamination and loss of aqueous ammonium sulfate solution can become substantial, especially at periods of peak fertilizer demand.
U.S. Pat. No. 3,930,832 discloses that corrosion of carbon steel by an aqueous solution of zinc nitrate, ammonium nitrate and urea is inhibited by incorporating therein an effective amount of ammonium thiosulfate.
U.S. Pat. No. 4,191,550 discloses that incorporation of a water-soluble thiosulfate into storage-stable liquid compositions of magnaesium nitrate, ammonium nitrate and urea satisfactorily provides protection for carbon steel equipment without deleterious effect on the stability or salt-out temperature of the composition.
Accordingly it is one object of this invention to provide a simple method and composition for corrosion inhibition of carbon steel equipment in contact with a aqueous ammonium sulfate solution.